Melting behaviour of americium-doped uranium dioxide

Abstract

a b s t r a c t (Uranium + americium) mixed oxides are considered as potential targets for americium transmutation in fast neutron reactors. Their thermophysical properties and notably their melting behaviour have not been assessed properly although required in order to evaluate the safety of these compounds under irradiation. In this study, we measured via laser heating, the melting points under inert atmosphere (Ar) of U 1Àx Am x O 2±d samples with x = 0.10, 0.15, 0.20. The obtained melting/solidification temperatures, measured here, indicate that under the current experimental conditions in the investigated AmO 2 content range, the solidus line of the (UO 2 + AmO 2 ) system follows with very good agreement the ideal solution behaviour. Accordingly, the observed liquidus formation temperature decreases from (3130 ± 20) K for pure UO 2 to (3051 ± 28) K for U 0.8 Am 0.2 O 2±d . The melted and quenched materials have been characterised by combining X-ray diffraction and X-ray absorption spectroscopy.

Fifteen Years of Radionuclide Research at the KIT Synchrotron Source in the Context of the Nuclear Waste Disposal Safety Case

“…This process has been observed by, e.g., D. Prieur et al in their study on Am/U oxide solid solution formation [12]. As discussed above, the resulting minor UO 2+x fraction is not detectable in the present work and might require a combination of spatially resolved and high (energy) resolution XAS techniques (i.e., U M-edge HERFD/PFY/HR-XANES, e.g., [66][67][68][69]) in future studies.…”

“…Since recoil-induced Am-cation displacement in the UO2 lattice is not to be expected, the necessary charge balance might occur via formation of Am(III)O7 11− moieties with oxygen vacancies in the cubic, eight-fold coordinated cation site of the fluorite structure. Alternatively, UO2 can act as redox buffer: Am(IV) → Am(III) / UO2 → UO2 + x (3) This process has been observed by, e.g., D. Prieur et al in their study on Am/U oxide solid solution formation [12]. As discussed above, the resulting minor UO2+x fraction is not detectable in the present work and might require a combination of spatially resolved and high (energy) resolution XAS techniques (i.e., U M-edge HERFD/PFY/HR-XANES, e.g., [66][67][68][69]) in future studies.…”

“…As SNF reprocessing residues (i.e., after fabrication of (U,Pu)O 2 mixed oxide fuels), MAs dominate the inventory of long-lived radionuclides, and thus suppression of their generation during reactor operation or conversion into mainly short-lived or stable isotopes after their extraction from SNF is considered to be beneficial. In France, the irradiation of U 1−x Am x O 2±δ compounds in a fast neutron reactor has been conceived as a reference process to study efficient MA burning, e.g., [12,13]. As the transmutation targets have to be present in the form of dense ceramic pellets, powder metallurgy processes with ball-milling steps have been found to be suitable, but generate large amounts of highly contaminant, sub-micron radioactive particles.…”

High-energy resolution X-ray spectroscopy at actinide M4,5 and ligand K edges: what we know, what we want to know, and what we can know

“…The DFT+U approach was used with the help of Quantum Espresso v. In case of Am-doped UO 2 , the situation was found to be different. It was reported that americium introduced into the UO 2 lattice is predominantly in the Am(III) state [111][112][113][114][115][116][117][118]…”

Using laser remote heating to simulate extreme thermal heat loads on nuclear fuels

“…In the field of nuclear fission research, there are several works dealing with the use of high power laser / material interactions for the investigation of the properties of fuel materials at high temperature, starting from the 80's [4,5]. Particularly, laser heating devices together with analysis diagnostics and temperature monitoring systems have been applied for the measurement of thermal properties (heat capacity, diffusivity, conductivity) [6] and thermodynamic properties (melting point, evaporation point, vapor pressure, equation of state) [7][8][9][10][11][12][13][14][15]. Combined laser heating with sample levitation and synchrotron x-rays has also allowed studying molten uranium dioxide structure at very high temperature (up to 3270K) [16].…”